Despite the coronavirus contagion, the “sell in May” proverb took a backseat last month as all key U.S. indexes added smart gains. The S&P 500 (up 3.6% past month), the Dow Jones (up 3.1% past month), the Nasdaq (up 5.1% past month) and the Russell 2000 (up 2.9% past month) – were all in the green (as of May 29, 2020). Rising hopes for a COVID-19 vaccine and the reopening of economies along with massive Fed and government stimulus propelled the markets higher.These are key financial and economic highlights from the month of May.Reopening of EconomiesBy now, all 50 states of the United States have reopened to some extent. Not just the United States, several global economies also started to open from May-end. Popular stay-at-home stocks saw their winning momentum waning a bit as investors started to bet in favor of easing lockdowns. Strengthening vaccine hopes and some upbeat economic indicators also added to the optimism.The key coronavirus casualty – the airlines sector – took off in May. U.S. Global Jets ETF JETS was down only 0.75 in May, while it added 9.8% in the past five days (as of May 29, 2020). Consumer-oriented ETFs like Consumer Discretionary Select Sector SPDR Fund XLY added 6.5% in May on easing social-distancing norms.Resurgence of U.S.-China Tensions, Wall Street UnscathedTensions between the United States and China resurfaced in May. President Donald Trump said that he is mulling over taking action against China as the Asian country enacted national security laws on Hong Kong. The legislation would impose on the autonomy of the Hong Kong region and endanger its special trade status with the United States.Apart from the Hong Kong issue, the U.S.-China relation worsened on President Trump’s repeated verbal attacks against China for its mishandling of the coronavirus contagion as well as Beijing’s treatment of minority Uighur Muslims in the Xinjiang region. The U.S. Senate passed a bill by unanimous consent recently to delist some Chinese corporations from U.S. exchanges. However, Wall Street does not seem to have priced in the Hong Kong tensions yet.Energy Market RalliesAfter crashing in mid-April, oil prices recovered in May on an improved demand outlook based on the reopening of economies. In fact, WTI crude oil spiked 88% in May, marking its best monthly performance since 1983, according to data from Bloomberg.United States Brent Oil Fund LP BNO (up 55.9%), United States Oil Fund LP USO (up 46.89%), SPDR SP Oil Gas Equipment Services ETF XES (up 25.1%), InfraCap MLP ETF AMZA (up 25.1%) and VanEck Vectors Oil Services ETF OIH (up 21.6%) were among the winners(read: Oil Price Rebound, USO ETF & More).Cannabis on a HighShares of cannabis-related stocks and ETFs surged in May following a report that some strains of medical marijuana are proving effective to treat coronavirus. The report indicates that medicinal marijuana could block up to 70% of the proteins used by the virus to infect cells.If this was not enough, Canada’s Aurora Cannabis agreed to buy U.S.-based CBD company Reliva in May, in order to enter the U.S. market. In any case, pot stocks became a winner in the pandemic as many cannabis dispensaries received “essential business” designations amid widespread COVID-19-related lockdowns and store closures. As a result, consumers hoarded medicinal and recreational cannabis.Global X Cannabis ETF POTX (up 27.7%), The Cannabis ETF THCX (up 26.96%) and AdvisorShares Pure Cannabis ETF YOLO (up 26.87%) all saw strong gains in the month (read: Cannabis ETF Tops in May: 5 Stocks That Led The Way).More Stimulus Optimism in Europe In late-May, the European Commission proposed a plan to borrow 750 billion euros ($826.5 billion) on the market and then disburse to EU countries. The fund will include 500 billion euros in grants and 250 billion euros in loans. This will help them recover from the coronavirus slump.Investors should note that apart from the latest stimulus plan, the ECB launched an $820 billion coronavirus package in March. Apart from this, the ECB restarted QE from November 2019 and has a negative interest in place (read: ETFs to Gain on ECB's Coronavirus Emergency Stimulus Rollout).Immediately after the announcement of stimulus proposal, Europe ETFs like First Trust Germany AlphaDEX Fund FGM, iShares MSCI Denmark ETF EDEN, iShares MSCI Sweden ETF EWD and ProShares MSCI Europe Dividend Growers ETF EUDV gained the most.Want key ETF info delivered straight to your inbox?Zacks’ free Fund Newsletter will brief you on top news and analysis, as well as top-performing ETFs, each week. Get it free >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report United States Oil ETF (USO): ETF Research Reports SPDR SP Oil Gas Equipment Services ETF (XES): ETF Research Reports United States Brent Oil ETF (BNO): ETF Research Reports InfraCap MLP ETF (AMZA): ETF Research Reports VanEck Vectors Oil Services ETF (OIH): ETF Research Reports ProShares MSCI Europe Dividend Growers ETF (EUDV): ETF Research Reports iShares MSCI Sweden ETF (EWD): ETF Research Reports First Trust Germany AlphaDEX ETF (FGM): ETF Research Reports iShares MSCI Denmark ETF (EDEN): ETF Research Reports AdvisorShares Pure Cannabis ETF (YOLO): ETF Research Reports The Cannabis ETF (THCX): ETF Research Reports Global X Cannabis ETF (POTX): ETF Research Reports To read this article on Zacks.com click here. Zacks Investment Research Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report